It has long been known in the art that certain biological, i.e. microbial, inoculants can be used with certain specific crops to facilitate the growth of crop plants or to assist the crops in resistance to particular pathogenic organisms. For example, it is quite common to inoculate soybean or other legumes at plantings with bacterial cultures of the genus Rhizobium, so that resulting Rhizobium cultures will nodulate within the roots of the soybean or other legume to form colonies which will fix nitrogen symbiotically for the plant as well as the bacteria.
It has also been proposed in the literature to co-cultivate microorganisms with other useful plants. For example, a method is described in U.S. Pat. No. 4,345,403 to Giovannetti to produce plants mycorrhizated with symbiotic fungi. Such symbiotic co-cultivations are sometimes used to help the plant growth and alternatively sometimes used to produce fungi for consumption.
It is also known that soils in many areas suppress certain plant diseases. The disease suppression may be caused by bacteria in the genus Pseudomonas which colonize root surfaces, according to Schroth, Milton N. et al., "Disease-Suppressive Soil And Root-Colonizing Bacteria", Science, Volume 216, Jun. 25, 1982.